QM Power and the SPARK Lab at University of Kentucky shared the combined results of a large-scale, multi-objective design optimization study, and lab testing of a prototype motor designed to meet the 2025 power density goals set by the US Department of Energy (DOE). The research demonstrated the high torque and speed capability of QM Power’s innovative permanent magnet (PM) motor technology.

This, combined with advanced manufacturing and cooling technologies, achieved a record-high 50kW/liter volumetric power density for traction applications such as electric vehicles (EV).

The announcement was made at the 2021 IEEE Energy Conversion Congress and Expo (ECCE) by the joint team of researchers including Dr. Madhav Manjrekar, SMIEEE, of QM Power, who also holds a tenured faculty position at University of North Carolina, Charlotte, and Dr. Dan M. Ionel, FIEEE, who serves as the inaugural L. Stanley Pigman Chair in Power at University of Kentucky, where he also directs the SPARK Lab.

As described in the paper presented at ECCE, the proposed very high power density PM motor has a PM-free castellated reluctance rotor, a modular stator having concentrated toroidal coils and circumstantially magnetized PMs. The robust rotor construction is very suitable for high-speed operation.

Exploded view of the proposed PM motor. The PM-free castellated rotor, modular stator, segmented PMs, and concentrated toroidal windings are the key features. Han et al.

In addition, since both the PMs and armature windings are placed on the stator and there is no overlapping between them, the design and implementation of the cooling system are simplified.

The toroidal windings are naturally concentrated; the copper slot fill is improved and the end coils are shortened compared to conventional distributed windings, which lead to reduced DC copper loss. The adjacent magnets are magnetized in the opposing way to provide the desired flux coupling for torque enhancement. The combination of stator PMs, rotor protrusions and stator winding layout plays a key role in determining the overall electromagnetic performance, such as average torque, torque ripple, and power factor.

The computational study was conducted at the SPARK Lab. An open frame lab prototype was designed and manufactured by QM Power. Tests and extensive simulations were conducted at University of North Carolina, Charlotte and at University of Kentucky to reveal the best outcome given trade-offs among efficiency, power density and power factor while achieving the DOE 2025 target.

In 2019 the US DOE established the 2025 goal as part of an ongoing effort to reduce dependency on resources such as fossil fuels and rare earth magnets. It represents an ambitious 89% reduction in motor volume compared to 2020 targets. This project is among the programs which the DOE's Vehicle Technologies Office deems to “have the potential to support radical new vehicle architectures by dramatic volume/space reductions and increased durability and reliability.”

Major challenges associated with existing designs include the overheating and demagnetization of the rotor during system operation. QM Power’s patented design employs no magnets in the rotor, thus minimizing these risks and enabling highly effective direct cooling of magnets in the stator.

The unique topology of this motor enables lighter, smaller electric motors which are more efficient and easier to manufacture. These motors are expected to offer superior performance in terms of torque production and achieve more miles per charging cycle, thus enabling electric transportation at much lower costs.

—Madhav Manjrekar

Resources

• Han P., Kesgin M. G., Ionel D. M., Gosalia R., Shah N., Flynn J. F., Goli C. S., Essakiappan S., and Manjrekar M. (2021) “Design Optimization of a Very High Power Density Motor with a Reluctance Rotor and a Modular Stator Having PMs and Toroidal Windings,” Proceedings, IEEE ECCE 2021, Vancouver, Canada, 7p pdf